Hi, I'm trying to calibrate the USRP so I can get true dBm readings out of it. I'm using an LFRX card with 16 decimation and a center frequency of 2 MHz so I can look at the range from DC - 4 MHz. I hooked up a signal generator and swept it through the DC - 4 MHz range at 100 kHz intervals and generated the plot here:
http://ice.cc.gt.atl.ga.us/usrp_adc_response.jpg The signal generator produced a -36 dBm signal for each frequency, and the y-axis of this plot is the output of the USRP's ADC in dB. (20 * log10 of the appropriate FFT bin for the frequency of interest, using an 8192 point FFT). My question is what is causing the particular shape of this response. I'm guessing it has to do with the CIC filter, but I can't seem to reconcile my output with the plots from this post on the CIC filter's response: http://lists.gnu.org/archive/html/discuss-gnuradio/2007-05/msg00191.html ...particularly this plot: http://www.nabble.com/file/8500/(0%20-%2032)MHz)%20CIC%20Frequency%20Response%20(CIC%20decimation%20%3D32).JPG Can someone please explain what's going on here? My end goal is to fit an equation to the dB "correction factor" I calculate in order to normalize across the entire 4 MHz chunk of spectrum. Thanks, Erich _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
